The effects of leaf deprivation on leaf-cutting ants and their mutualistic fungus

1. When leaf-cutting ants were deprived of leaves for 5 days, they increased their consumption rates of 'staphylae', the nutritive bodies produced by their mutualistic fungus. They also pruned their fungus garden more intensively, presumably stimulating increased staphyla production.
2. Depriving fungus gardens of leaves for 5 days led to greater rates of staphyla production compared with control gardens. The rate of substrate exhaustion also increased, possibly because of this increased staphyla production, which led to greater removal of fungal resources by the ants.
3. The availability of leaf substrate directly affected staphyla production by the fungus garden. When leaf fragments were inserted into fungus garden samples, staphyla production was depressed, suggesting that the fungus can allocate resources either to hyphal colonization of fresh substrate or to staphyla production.
4. Under conditions of leaf deprivation, food production for the ants effectively increased, due to the combined effects of increased pruning by the ants and the response of the fungus to lack of substrate. This will allow nests to survive for long periods in the field when forage availability is reduced.
5. Exposing parts of the colony to the stress of leaf deprivation showed that there is a high level of flexibility in the fungus garden's ability to produce staphylae. This may be important during the cyclic production of broods, when demands for larval food will fluctuate widely. Under normal conditions, the optimal strategy may be for the fungus garden to have a moderate rate of production with a low rate of turnover, unless demand for staphylae increases dramatically.